For example, in a winding device of a long object having a belt shape or a string shape (including a rewinding function), a winding barrel (also referred to as a drum or a spool) around which the long object is wound performs a rotary motion relative to a supporting unit rotatably supporting the winding barrel. In the device that performs such relative motion, in a case where the long object is fully extended or where the winding barrel is stopped during winding or rewinding, a large load is applied to the device and to the long object, whereby it is preferred that an energy absorption device be disposed between objects that are performing the relative motion. A representative example of such winding device is a seat belt retractor used in a seat belt device (see, for example, Patent Literature 1 or 2).
Patent Literature 1 discloses a seat belt retractor having a torsion bar and a wire disposed between a winding drum and a ratchet gear, which rotate relative to each other. By using such seat belt retractor, it is possible to absorb energy that may be generated between the winding drum and the ratchet gear by torsional deformation of the torsion bar and sliding deformation of the wire, and it is also possible to change energy absorption characteristics by varying a drawing load required for causing the sliding deformation of the wire.
Patent Literature 2 discloses a force-limiting device for a motor vehicle having ring disks (1 and 3) and an oscillating part (2) disposed between objects rotating relative to each other. By using such device, when the oscillating part (2) rotates relative to the ring disks (1 and 3), a protrusion (5) formed in the oscillating part (2) alternately contacts protrusions (7 and 8) formed in the ring disks (1 and 3) while oscillating, whereby it is possible to absorb energy generated between the objects rotating relative to each other. More specifically, in this device, kinetic energy changes with a rotation speed of the oscillating part (2), whereby it is possible to increase an energy absorption amount as the rotation speed of the oscillating part (2) increases.